The present invention relates to processes for producing 5-alkoxy-2,4-dinitroalkylbenzenes of the general formula (I) ##STR2## where R.sup.1 is a branched or unbranched C.sub.1 to C.sub.4 alkyl group and R is a branched or unbranched C.sub.1 to C.sub.6 alkyl group, a C.sub.2 to C.sub.4 hydroxyalkyl group or a C.sub.3 to C.sub.4 dihydroxyalkyl group, which can be used as dye precursor, etc., e.g. for hair dyes.
A number of processes for producing 5-alkoxy-2,4-dinitroalkylbenzenes of formula (I) are already known from the relevant literature. However, these processes are unsatisfactory in many respects.
For example, J. F. Corbett, Journal of the Chemical Society Perkin II, page 999 (1972), describes a process for producing 5-methoxy-2,4-dinitrotoluene in which 5-chloro-2,4-dinitrotoluene and methanol are heated under reflux in the presence of potassium hydroxide. However, the yield in this process is unsatisfactory.
Further, DE-OS 3 622 784 describes a process for the production of 5-alkoxy-2,4-dinitroalkylbenzenes in which 5-alkyl-2,4-dinitrophenol is reacted in an appropriate solvent with a suitable alkyl halide in the presence of a base and the product is then precipitated by adding water. Although the alkylation in this process produces satisfactory yields (50 to 77%), the overall production method involves some disadvantages. For example, the starting material required for this method must be produced by a three-step synthesis starting with 3-methyl-6-nitrophenol by introducing a mesyl protective group, nitration and subsequent separation of the protective group with a total yield of roughly 76%. Further, the alkyl halides, which are not without disadvantages, must be used as reagents for producing the alkyl compounds. Although the process described above for producing 5-alkoxy-2,4-dinitroalkylbenzenes of the general formula (I) can be carried out with a satisfactory yield technically, it nevertheless has disadvantages in economical and ecological respects. The large number of required reaction steps and the type of reagents that are used necessitate a high input of energy for carrying out the reactions. In addition, waste products are produced in every reaction step (by-products and solvent) which must be worked up and disposed of in an expensive manner to prevent additional environmental loading. These disadvantages are also shared in great measure by the process according to Corbett in which the proportion of by-products is greater than the proportion of desired reaction products.